When I try watching videos with internet explorer it tells me I need to update my flash player, but I do have the latest version (11.3.300.268) and even when following the installing-link nothing changes about it.

Has anyone ever run into this problem and knows a way how to solve it?

From what I know, everything that starts with "Mein Führer" is for no good

On the serious side of the problem now... I had 2 or 3 solutions about this but you've tried them all... Maybe there's a problem with your Youtube Profile - someone is trying to get you banned? I know that many Youtube videos are banned for German users, but that's just ridiculous.

(But you're right about one thing..the amount of videos getting blocked in Germany only surely is ridiculous)

IIRC, there were a number of privacy and data protection laws that have been brought to bare in court recently that pretty much guaranteed that would happen. From their perspective, It's far easier to pull out of a market altogether (or block a lot of stuff) than to make significant changes to your product - especially if they require you to hire an unfeasibly large number of people to look through things by hand as they're uploaded.

If you've only been having trouble for a few days then try a system restore to a point when you weren't having trouble assuming you haven't done anything else significant since then.

"The people cannot be [...] always, well informed. The part which is wrong will be discontented, in proportion to [...] the facts they misconceive. If they remain quiet under such misconceptions, it is lethargy, the forerunner of death to public liberty. What country can preserve its liberties, if it's rulers are not warned [...] that this people preserve the spirit of resistance? The tree of liberty must be refreshed from time to time, with the blood of patriots and tyrants."-Thomas Jefferson

From what I can guess, it's an issue with flash itself, how youtube is using flash, or both. I've been running into this issue for a month or two when I start firefox with youtube tabs open (especially since I like to load loooooooooong playlists and watch them over a week or two.) The videos will often say "error loading your video", though refreshing works for me 99 times out of 100.

Usually, I find that stuff like this is thoroughly brought to google's/adobe's attention...and gets fixed in time.

Still gotta re-watch any pre-roll advertisements when you reload the page though (including when youtube decides the page has to be refreshed when you exit out of fullscreen) You'd think setting a cookie to determine when an ad has been watched that gets unset/reset every time you load a new video wouldn't be that hard to do...